1. Field of the Invention
The present invention relates to a method and apparatus for digital data management, and in particular to decrypting digital data.
2. Background Art
In the information oriented society of today, database systems are becoming wide spread in which it is possible to use various types of data, stored independently by each computer in the past, by connecting computers via communication lines.
In such a database system, the information handled up to this point has been conventionally coded information that can be processed by computer, and that contains a relatively small amount of information and monochrome binary data, such as facsimile information at the most. It is not possible to handle data containing a relatively large amount of information, such as data for natural pictures or animation.
With the rapid progress of digital processing techniques for various types of electrical signals, a technique is under development for digital processing of picture signals other than binary data, handled only as analog signals in the past.
By digitizing the picture signal, it is possible to handle a picture signal, such as television signal, by computer. As a technique of the future, attention is now focused on “multimedia systems”, which can simultaneously handle the data processed by computers and digitized picture data. Because the picture data contains an overwhelmingly large amount of information compared with character data and audio data, it is difficult to store, transfer or process the picture data by computer. For this reason, techniques for compressing and expanding picture data have been developed. Further, several standards for compression/expansion of picture data have been established. For example, the following standards have been established as common standards: JPEG (Joint Photographic image coding Experts Group) standards for still pictures, H.261 standards for television conferences, MPEG1 (Moving Picture image coding Experts Group 1) standards for picture accumulation, and MPEG2 standards to cope with current television broadcasting and high definition television broadcasting. By implementing these new techniques, it is now possible to transmit digital picture data in real time.
For analog data, which has been widely used in the past, the control of copyrights during processing has not been an important issue because the quality of the analog data deteriorates each time the data is stored, copied, edited or transferred. However, the quality of digital data does not deteriorate even when the data is repeatedly stored, copied, edited or transferred. Therefore, the management and control of copyrights during processing of digital data is an important issue.
Up to now, there has been no adequate method for management and control of copyrights for digital data. It has been managed and controlled merely by copyright law or by contracts. In copyright law, only compensation for digital sound and picture recording devices has been prescribed.
It is possible not only to refer to the content of a database, but also to effectively utilize the data obtained from the database by storing, copying or editing the data, and also transferring the edited data to other persons or to the database with the edited data registered as new data.
In a conventional database system, only character data is handled. However, in multimedia systems, sound data and picture data, which are originally analog data, are digitized and used as part of the database in addition to the other data in the database, such as character data.
Under such circumstances, it is an important question as to how to handle copyrights of the data in the database. However, there are no means in the prior art for copyright management and control of such actions as copying, editing, transferring, etc., of data.
A system for executing copyright control by using encrypted data and obtaining a permit key from a key control center via public telephone lines is disclosed in Japanese Patent Application 4-199942 (U.S. Ser. No. 08/098,415) and Japanese Patent Application 4-289074 (U.S. Ser. No. 08/143,912) of the present inventors. A device for this purpose is disclosed in Japanese Patent Application 4-276941 (U.S. Ser. No. 08/135,634), also of the present inventors.